System and method for ultra wideband radio wireless network

ABSTRACT

A virtual wireless local area network system and method utilizing impulse radio wherein transmission rates (bit rates) can vary according to the impulse radio transmission quality (signal to noise ratio) and wherein the position of the user can be determined and said user can be directed to an area of greater transmission rates and wherein a plurality of impulse radio portals can be utilized and switched between to maintain high levels of transmission rates while a user is moving within a predetermined area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a virtual wireless local areanetwork system and method. More particularly, the present inventionprovides a virtual wireless local area network system and methodutilizing impulse radio.

2. Background of the Invention and Related Art

Mobile computing and communication has dramatically improved in recentyears. Computers have become much smaller and battery life has improvedenabling truly mobile computing and communications. This has come aboutbecause of the demand in place to be able to be mobile and yet have thesame computing and communicating power as if one were located in one'soffice.

Further, the ability to share information among people and computers hasspawned immense improvements in Local Area and Wide Area Networks. Thegreatest example of this is the Internet. People from all over the worldnow have the ability to communicate and share information throughout theworld. Notwithstanding these improvements, truly mobile computing andcommunicating is still lacking. In an office building environment, ifone desires to go from room to room it is very inconvenient to bringeven the lightest computer with them. Further, even though dockingstations with notebook computers enable users to “take their office withthem” to a certain extent, it is still difficult to undock a notebookcomputer and reboot it up if you just are leaving the office for a shortmeeting in another office. Also, many times one would like to keep theiroffice computer running and have a means of accessing it and it'scomputing power remotely. Having the ability to communicate with one'scomputer could also enable remote data processing, remote voicecommunication, remote email communication and any other voice or datafunctions presently available in a communication and computingenvironment.

Efforts have been made to create wireless local area networks, but withlimited success. Traditional wireless communication means are subject tomultipath problems as described below. Further, if one comes upon anarea of very poor RF transmissive properties, it is impossible for themto know which way to move in order to go to an area of greatertransmissive properties.

Thus there is a strong need in the mobile communication and computingindustry for a system of method of wireless data transfer within apredetermined area and wherein the location and identity of the devicecan be ascertained thus enabling intelligent network connectivity.

SUMMARY OF THE INVENTION

The present invention provides a novel virtual wireless local areanetwork that can automatically vary the data rate according to thepropagation environment and requirements of the user.

It is a further object of the present invention to provide a novelvirtual wireless local area network that can automatically vary the datarate according to the propagation environment and requirements of theuser, to determine the position and identity of the user, and to therebydirect the user to an area of improved propagation characteristics whenhigher data rates are required.

It is another object of the present invention to provide a novel virtualwireless local area network that can automatically vary the data rateaccording to the propagation environment and requirements of the user,to determine the position and identity of the user, and to thereby allowthe user to access their base computing and communication systems.

It is another object of the present invention to provide impulse radioportals throughout a predetermined area to allow wireless connectivitythroughout said predetermined area; placing more impulse radio portalsspaced more closely together if greater data rates are required andfewer impulse radio portals spaced farther apart if lower data rateswill be needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1A illustrates a representative Gaussian Monocycle waveform in thetime domain;

FIG. 1B illustrates the frequency domain amplitude of the GaussianMonocycle of FIG. 1A;

FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A;

FIG. 2B illustrates the frequency domain amplitude of the waveform ofFIG. 2A;

FIG. 3 illustrates the frequency domain amplitude of a sequence of timecoded pulses;

FIG. 4 illustrates a typical received signal and interference signal;

FIG. 5A illustrates a typical geometrical configuration giving rise tomultipath received signals;

FIG. 5B illustrates exemplary multipath signals in the time domain;

FIGS. 5C-5E illustrate a signal plot of various multipath environments.

FIG. 5F illustrates the Rayleigh fading curve associated withnon-impulse radio transmissions in a multipath environment.

FIG. 5G illustrates a plurality of multipaths with a plurality ofreflectors from a transmitter to a receiver.

FIG. 5H graphically represents signal strength as volts vs. time in adirect path and multipath environment.

FIG. 6 illustrates a representative impulse radio transmitter functionaldiagram;

FIG. 7 illustrates a representative impulse radio receiver functionaldiagram;

FIG. 8A illustrates a representative received pulse signal at the inputto the correlator;

FIG. 8B illustrates a sequence of representative impulse signals in thecorrelation process;

FIG. 9 illustrates the potential locus of results as a function of thevarious potential template time positions;

FIG. 10 is an illustration of one embodiment of the present inventionwherein a mobile unit is connected wirelessly to an impulse radio portalwhich is interfaced with a Local Area Network (LAN) or Wide Area Network(WAN).

FIG. 11 illustrates one embodiment of an impulse radio portal whichcommunicates wirelessly to a mobile unit and is interfaced to a WAN orLAN.

FIG. 12 is a flow chart illustrating the method of remote computing andcommunicating within a predetermined area covered by a plurality ofimpulse radio portals.

DETAILED DESCRIPTION OF THE EMBODIMENTS Overview of the Invention

The present invention will now be described more fully in detail withreference to the accompanying drawings, in which the preferredembodiments of the invention are shown. This invention should not,however, be construed as limited to the embodiments set forth herein;rather, they are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in art. Like numbers refer to like elements throughout.

Recent advances in communications technology have enabled an emerging,revolutionary ultra wideband technology (UWB) called impulse radiocommunications systems (hereinafter called impulse radio). To betterunderstand the benefits of impulse radio to the present invention, thefollowing review of impulse radio follows Impulse radio was first fullydescribed in a series of patents, including U.S. Pat. Nos. 4,641,317(issued Feb. 3, 1987), 4,813,057 (issued Mar. 14, 1989), 4,979,186(issued Dec. 18, 1990) and 5,363,108 (issued Nov. 8, 1994) to Larry W.Fullerton. A second generation of impulse radio patents include U.S.Pat. Nos. 5,677,927 (issued Oct. 14, 1997), 5,687,169 (issued Nov. 11,1997) and 5,832,035 (issued Nov. 3, 1998) to Fullerton et al.

Uses of impulse radio systems are described in U.S. patent applicationSer. No. 09/332,502 (Attorney Docket No. 1659.0720000), entitled,“System and Method for Intrusion Detection Using a Time Domain RadarArray,” and U.S. patent application Ser. No. 09/332,503 (Attorney DocketNo. 1659.0670000), entitled, “Wide Area Time Domain Radar Array,” bothfiled on Jun. 14, 1999 and both of which are assigned to the assignee ofthe present invention. All of the above patent documents areincorporated herein by reference.

Impulse Radio Basics

This section is directed to technology basics and provides the readerwith an introduction to impulse radio concepts, as well as otherrelevant aspects of communications theory. This section includessubsections relating to waveforms, pulse trains, coding for energysmoothing and channelization, modulation, reception and demodulation,interference resistance, processing gain, capacity, multipath andpropagation, distance measurement, and qualitative and quantitativecharacteristics of these concepts. It should be understood that thissection is provided to assist the reader with understanding the presentinvention, and should not be used to limit the scope of the presentinvention.

Impulse radio refers to a radio system based on short, low duty cyclepulses. An ideal impulse radio waveform is a short Gaussian monocycle.As the name suggests, this waveform attempts to approach one cycle ofradio frequency (RF) energy at a desired center frequency. Due toimplementation and other spectral limitations, this waveform may bealtered significantly in practice for a given application. Mostwaveforms with enough bandwidth approximate a Gaussian shape to a usefuldegree.

Impulse radio can use many types of modulation, including AM, time shift(also referred to as pulse position) and M-ary versions. The time shiftmethod has simplicity and power output advantages that make itdesirable. In this document, the time shift method is used as anillustrative example.

In impulse radio communications, the pulse-to-pulse interval can bevaried on a pulse-by-pulse basis by two components: an informationcomponent and a pseudo-random code component. Generally, conventionalspread spectrum systems make use of pseudo-random codes to spread thenormally narrow band information signal over a relatively wide band offrequencies. A conventional spread spectrum receiver correlates thesesignals to retrieve the original information signal. Unlike conventionalspread spectrum systems, the pseudo-random code for impulse radiocommunications is not necessary for energy spreading because themonocycle pulses themselves have an inherently wide bandwidth. Instead,the pseudo-random code is used for channelization, energy smoothing inthe frequency domain, resistance to interference, and reducing theinterference potential to nearby receivers.

The impulse radio receiver is typically a direct conversion receiverwith a cross correlator front end in which the front end coherentlyconverts an electromagnetic pulse train of monocycle pulses to abaseband signal in a single stage. The baseband signal is the basicinformation signal for the impulse radio communications system. It isoften found desirable to include a subcarrier with the baseband signalto help reduce the effects of amplifier drift and low frequency noise.The subcarrier that is typically implemented alternately reversesmodulation according to a known pattern at a rate faster than the datarate. This same pattern is used to reverse the process and restore theoriginal data pattern just before detection. This method permitsalternating current (AC) coupling of stages, or equivalent signalprocessing to eliminate direct current (DC) drift and errors from thedetection process. This method is described in detail in U.S. Pat. No.5,677,927 to Fullerton et al.

In impulse radio communications utilizing time shift modulation, eachdata bit typically time position modulates many pulses of the periodictiming signal. This yields a modulated, coded timing signal thatcomprises a train of identically shaped pulses for each single data bit.The impulse radio receiver integrates multiple pulses to recover thetransmitted information.

Waveforms

Impulse radio refers to a radio system based on short, low duty cyclepulses. In the widest bandwidth embodiment, the resulting waveformapproaches one cycle per pulse at the center frequency. In more narrowband embodiments, each pulse consists of a burst of cycles usually withsome spectral shaping to control the bandwidth to meet desiredproperties such as out of band emissions or in-band spectral flatness,or time domain peak power or burst off time attenuation.

For system analysis purposes, it is convenient to model the desiredwaveform in an ideal sense to provide insight into the optimum behaviorfor detail design guidance. One such waveform model that has been usefulis the Gaussian monocycle as shown in FIG. 1A. This waveform isrepresentative of the transmitted pulse produced by a step function intoan ultra-wideband antenna. The basic equation normalized to a peak valueof 1 is as follows:

${f_{mono}(t)} = {\sqrt{}( \frac{t}{\sigma} )^{\frac{- t^{2}}{2\sigma^{2}}}}$

Where,

σ is a time scaling parameter,

t is time,

f_(mono)(t) is the waveform voltage, and

e is the natural logarithm base.

The frequency domain spectrum of the above waveform is shown in FIG. 1B.The corresponding equation is:

${F_{mono}(f)} = {( {2\pi} )^{\frac{3}{2}}\sigma \; f\; ^{{- 2}{({{\pi\sigma}\; f})}^{2}}}$

The center frequency (f_(c)), or frequency of peak spectral density is:

$f_{c} = \frac{1}{2{\pi\sigma}}$

These pulses, or bursts of cycles, may be produced by methods describedin the patents referenced above or by other methods that are known toone of ordinary skill in the art. Any practical implementation willdeviate from the ideal mathematical model by some amount. In fact, thisdeviation from ideal may be substantial and yet yield a system withacceptable performance. This is especially true for microwaveimplementations, where precise waveform shaping is difficult to achieve.These mathematical models are provided as an aid to describing idealoperation and are not intended to limit the invention. In fact, anyburst of cycles that adequately fills a given bandwidth and has anadequate an-off attenuation ratio for a given application will serve thepurpose of this invention.

A Pulse Train

Impulse radio systems can deliver one or more data bits per pulse;however, impulse radio systems more typically use pulse trains, notsingle pulses, for each data bit. As described in detail in thefollowing example system, the impulse radio transmitter produces andoutputs a train of pulses for each bit of information.

Prototypes built by the inventors have pulse repetition frequenciesincluding 0.7 and 10 megapulses per second (Mpps, where each megapulseis 10⁶ pulses). FIGS. 2A and 2B are illustrations of the output of atypical 10 Mpps system with uncoded, unmodulated, 0.5 nanosecond (xis)pulses 102. FIG. 2A shows a time domain representation of this sequenceof pulses 102. FIG. 2B, which shows 60 MHZ at the center of the spectrumfor the waveform of FIG. 2A, illustrates that the result of the pulsetrain in the frequency domain is to produce a spectrum comprising a setof lines 204 spaced at the frequency of the 10 Mpps pulse repetitionrate. When the full spectrum is shown, the envelope of the line spectrumfollows the curve of the single pulse spectrum 104 of FIG. 1B. For thissimple uncoded case, the power of the pulse train is spread amongroughly two hundred comb lines. Each comb line thus has a small fractionof the total power and presents much less of an interference problem toreceiver sharing the band.

It can also be observed from FIG. 2A that impulse radio systemstypically have very low average duty cycles resulting in average powersignificantly lower than peak power. The duty cycle of the signal in thepresent example is 0.5%, based on a 0.5 ns pulse in a 100 ns interval.

Coding for Energy Smoothing and Channelization

For high pulse rate systems, it may be necessary to more finely spreadthe spectrum than is achieved by producing comb lines. This may be doneby pseudo-randomly positioning each pulse relative to its nominalposition.

FIG. 3 is a plot illustrating the impact of a pseudo-noise (PN) codedither on energy distribution in the frequency domain (A pseudo-noise,or PN code is a set of time positions defining the pseudo-randompositioning for each pulse in a sequence of pulses). FIG. 3, whencompared to FIG. 2B, shows that the impact of using a PN code is todestroy the comb line structure and spread the energy more uniformly.This structure typically has slight variations which are characteristicof the specific code used.

The PN code also provides a method of establishing independentcommunication channels using impulse radio. PN codes can be designed tohave low cross correlation such that a pulse train using one code willseldom collide on more than one or two pulse positions with a pulsestrain using another code during any one data bit time. Since a data bitmay comprise hundreds of pulses, this represents a substantialattenuation of the unwanted channel.

Modulation

Any aspect of the waveform can be modulated to convey information.Amplitude modulation, phase modulation, frequency modulation, time shiftmodulation and M-ary versions of these have been proposed. Both analogand digital forms have been implemented. Of these, digital time shiftmodulation has been demonstrated to have various advantages and can beeasily implemented using a correlation receiver architecture.

Digital time shift modulation can be implemented by shifting the codedtime position by an additional amount (that is, in addition to PN codedither) in response to the information signal. This amount is typicallyvery small relative to the PN code shift. In a 10 Mpps system with acenter frequency of 2 GHz., for example, the PN code may command pulseposition variations over a range of 100 ns; whereas, the informationmodulation may only deviate the pulse position by 150 ps.

Thus, in a pulse train of n pulses, each pulse is delayed a differentamount from its respective time base clock position by an individualcode delay amount plus a modulation amount, where n is the number ofpulses associated with a given data symbol digital bit.

Modulation further smooths the spectrum, minimizing structure in theresulting spectrum.

Reception and Demodulation

Clearly, if there were a large number of impulse radio users within aconfined area, there might be mutual interference. Further, while the PNcoding minimizes that interference, as the number of users rises, theprobability of an individual pulse from one user's sequence beingreceived simultaneously with a pulse from another user's sequenceincreases. Impulse radios are able to perform in these environments, inpart, because they do not depend on receiving every pulse. The impulseradio receiver performs a correlating, synchronous receiving function(at the RF level) that uses a statistical sampling and combining of manypulses to recover the transmitted information.

Impulse radio receivers typically integrate from 1 to 1000 or morepulses to yield the demodulated output. The optimal number of pulsesover which the receiver integrates is dependent on a number ofvariables, including pulse rate, bit rate, interference levels, andrange.

Interference Resistance

Besides channelization and energy smoothing, the PN coding also makesimpulse radios highly resistant to interference from all radiocommunications systems, including other impulse radio transmitters. Thisis critical as any other signals within the band ccupied by an impulsesignal potentially interfere with the impulse radio. Since there arecurrently no unallocated bands available for impulse systems, they mustshare spectrum with other conventional radio systems without beingadversely affected. The PN code helps impulse systems discriminatebetween the intended impulse transmission and interfering transmissionsfrom others.

FIG. 4 illustrates the result of a narrow band sinusoidal interferencesignal 402 overlaying an impulse radio signal 404. At the impulse radioreceiver, the input to the cross correlation would include the narrowband signal 402, as well as the received ultrawide-band impulse radiosignal 404. The input is sampled by the cross correlator with a PNdithered template signal 406. Without PN coding, the cross correlationwould sample the interfering signal 402 with such regularity that theinterfering signals could cause significant interference to the impulseradio receiver. However, when the transmitted impulse signal is encodedwith the PN code dither (and the impulse radio receiver template signal406 is synchronized with that identical PN code dither) the correlationsamples the interfering signals pseudo-randomly. The samples from theinterfering signal add incoherently, increasing roughly according tosquare root of the number of samples integrated; whereas, the impulseradio samples add coherently, increasing directly according to thenumber of samples integrated. Thus, integrating over many pulsesovercomes the impact of interference.

Processing Gain

Impulse radio is resistant to interference because of its largeprocessing gain. For typical spread spectrum systems, the definition ofprocessing gain, which quantifies the decrease in channel interferencewhen wide-band communications are used, is the ratio of the bandwidth ofthe channel to the bit rate of the information signal. For example, adirect sequence spread spectrum system with a 10 kHz informationbandwidth and a 10 MHZ channel bandwidth yields a processing gain of1000 or 30 dB. However, far greater processing gains are achieved withimpulse radio systems, where for the same 10 KHz information bandwidthis spread across a much greater 2 GHz. channel bandwidth, thetheoretical processing gain is 200,000 or 53 dB.

Capacity

It has been shown theoretically, using signal to noise arguments, thatthousands of simultaneous voice channels are available to an impulseradio system as a result of the exceptional processing gain, which isdue to the exceptionally wide spreading bandwidth.

For a simplistic user distribution, with N interfering users of equalpower equidistant from the receiver, the total interference signal tonoise ratio as a result of these other users can be described by thefollowing equation:

$V_{tot}^{2} = \frac{N\; \sigma^{2}}{\sqrt{Z}}$

Where V² _(tot) is the total interference signal to noise ratiovariance, at the receiver;

N is the number of interfering users;

σ² is the signal to noise ratio variance resulting from one of theinterfering signals with a single pulse cross correlation; and

Z is the number of pulses over which the receiver integrates to recoverthe modulation.

This relationship suggests that link quality degrades gradually as thenumber of simultaneous users increases. It also shows the advantage ofintegration gain. The number of users that can be supported at the sameinterference level increases by the square root of the number of pulsesintegrated.

Multipath and Propagation

One of the striking advantages of impulse radio is its resistance tomultipath fading effects. Conventional narrow band systems are subjectto multipath through the Rayleigh fading process, where the signals frommany delayed reflections combine at the receiver antenna according totheir seemingly random relative phases. This results in possiblesummation or possible cancellation, depending on the specificpropagation to a given location. This situation occurs where the directpath signal is weak relative to the multipath signals, which representsa major portion of the potential coverage of a radio system. In mobilesystems, this results in wild signal strength fluctuations as a functionof distance traveled, where the changing mix of multipath signalsresults in signal strength fluctuations for every few feet of travel.

Impulse radios, however, can be substantially resistant to theseeffects. Impulses arriving from delayed multipath reflections typicallyarrive outside of the correlation time and thus can be ignored. Thisprocess is described in detail with reference to FIGS. 5A and 5B. InFIG. 5A, three propagation paths are shown. The direct path representingthe straight line distance between the transmitter and receiver is theshortest. Path 1 represents a grazing multipath reflection, which isvery close to the direct path. Path 2 represents a distant multipathreflection. Also shown are elliptical (or, in space, ellipsoidal) tracesthat represent other possible locations for reflections with the sametime delay.

FIG. 5B represents a time domain plot of the received waveform from thismultipath propagation configuration. This figure comprises three doubletpulses as shown in FIG. 1A. The direct path signal is the referencesignal and represents the shortest propagation time. The path 1 signalis delayed slightly and actually overlaps and enhances the signalstrength at this delay value. Note that the reflected waves are reversedin polarity. The path 2 signal is delayed sufficiently that the waveformis completely separated from the direct path signal. If the correlatortemplate signal is positioned at the direct path signal, the path 2signal will produce no response. It can be seen that only the multipathsignals resulting from very close reflectors have any effect on thereception of the direct path signal. The multipath signals delayed lessthan one quarter wave (one quarter wave is about 1.5 inches, or 3.5 cmat 2 GHz center frequency) are the only multipath signals that canattenuate the direct path signal. This region is equivalent to the firstFresnel zone familiar to narrow band sysetms designers. Impulse radio,however, has no further nulls in the higher Fresnel zones. The abilityto avoid the highly variable attenuation from multipath gives impulseradio significant performance advantages.

FIG. 5A illustrates a typical multipath situation, such as in abuilding, where there are many reflectors 5A04, 5A05 and multiplepropagation paths 5A02, 5A01. In this figure, a transmitter TX 5A06transmits a signal which propagates along the multiple propagation paths5A02, 5A04 to receiver RX 5A08, where the multiple reflected signals arecombined at the antenna.

FIG. 5B illustrates a resulting typical received composite pulsewaveform resulting from the multiple reflections and multiplepropagation paths 5A01, 5A02. In this figure, the direct path signal5A01 is shown as the first pulse signal received. The multiple reflectedsignals (“multipath signals”, or “multipath”) comprise the remainingresponse as illustrated.

FIGS. 5C, 5D, and 5E represent the received signal from a TM-UWBtransmitter in three different multipath environments. These figures arenot actual signal plots, but are hand drawn plots approximating typicalsignal plots. FIG. 5C illustrates the received signal in a very lowmultipath environment. This may occur in a building where the receiverantenna is in the middle of a room and is one meter from thetransmitter. This may also represent signals received from somedistance, such as 100 meters, in an open field where there are noobjects to produce reflections. In this situation, the predominant pulseis the first received pulse and the multipath reflections are too weakto be significant. FIG. 5D illustrates an intermediate multipathenvironment. This approximates the response from one room to the next ina building. The amplitude of the direct path signal is less than in FIG.5C and several reflected signals are of significant amplitude. (Notethat the scale has been increased to normalize the plot.) FIG. 5Eapproximates the response in a severe multipath environment such as:propagation through many rooms; from corner to corner in a building;within a metal cargo hold of a ship; within a metal truck trailer; orwithin an intermodal shipping container. In this scenario, the main pathsignal is weaker than in FIG. 5D. (Note that the scale has beenincreased again to normalize the plot.) In this situation, the directpath signal power is small relative to the total signal power from thereflections.

An impulse radio receiver in accordance with the present invention canreceive the signal and demodulate the information using either thedirect path signal or any multipath signal peak having sufficient signalto noise ratio.

Thus, the impulse radio receiver can select the strongest response fromamong the many arriving signals. In order for the signals to cancel andproduce a null at a given location, dozens of reflections would have tobe cancelled simultaneously and precisely while blocking the directpath—a highly unlikely scenario. This time separation of mulitipathsignals together with time resolution and selection by the receiverpermit a type of time diversity that virtually eliminates cancellationof the signal. In a multiple correlator rake receiver, performance isfurther improved by collecting the signal power from multiple signalpeaks for additional signal to noise performance.

Where the system of FIG. 5A is a narrow band system and the delays aresmall relative to the data bit time, the received signal is a sum of alarge number of sine waves of random amplitude and phase. In theidealized limit, the resulting envelope amplitude has been shown tofollow a Rayleigh probability distribution as follows:

${p(r)} = {\frac{1}{\sigma^{2}}{\exp ( \frac{- r^{2}}{2\sigma^{2}} )}}$

where r is the envelope amplitude of the combined multipath signals, and

2σ² is the RMS power of the combined mulitpath signals.

This distribution shown in FIG. 5F. It can be seen in FIG. 5F that 10%of the time, the signal is more than 16 dB attenuated. This suggeststhat 16 dB fade margin is needed to provide 90% link availability.Values of fade margin from 10 to 40 dB have been suggested for variousnarrow band systems, depending on the required reliability. Thischaracteristic has been the subject of much research and can bepartially improved by such techniques as antenna and frequencydiversity, but these techniques result in additional complexity andcost.

In a high multipath environment such as inside homes, offices,warehouses, automobiles, trailers, shipping containers, or outside inthe urban canyon or other situations where the propagation is such thatthe received signal is primarily scattered energy, impulse radio,according to the present invention, can avoid the Rayleigh fadingmechanism that limits performance of narrow band systems. This isillustrated in FIGS. 5G and 5H in a transmit and receive system in ahigh multipath environment 5G00, wherein the transmitter 5G06 transmitsto receiver 5G08 with the signals reflecting off reflectors 5G03 whichform multipaths 5G02. The direct path is illustrated as 5G01 with thesignal graphically illustrated at 5H02 with the vertical axis being thesignal strength in volts and horizontal axis representing time innanoseconds. Multipath signals are graphically illustrated at 5H04.

Distance Measurement and Position Location

Impulse systems can measure distances to extremely fine resolutionbecause of the absence of ambiguous cycles in the waveform. Narrow bandsystems, on the other hand, are limited to the modulation envelope andcannot easily distinguish precisely which RF cycle is associated witheach data bit because the cycle-to-cycle amplitude differences are sosmall they are masked by link or system noise. Since the impulse radiowaveform has no multi-cycle ambiguity, this allows positivedetermination of the waveform position to less than awavelength—potentially, down to the noise floor of the system. This timeposition measurement can be used to measure propagation delay todetermine link distance, and once link distance is known, to transfer atime reference to an equivalently high degree of precision. Theinventors of the present invention have built systems that have shownthe potential for centimeter distance resolution, which is equivalent toabout 30 ps of time transfer resolution. See, for example, commonlyowned, co-pending application Ser. Nos. 09/045,929, filed Mar. 23, 1998,titled “Ultrawide-Band Position Determination System and Method”, and09/083,993, filed May 26, 1998, titled “System and Method for DistanceMeasurement by Inphase and Quadrature Signals in a Radio System”, bothof which are incorporated herein by reference. Finally, distancemeasuring and position location using impulse radio using a plurality ofdistance architectures is enabled in co-pending and commonly ownedapplication Ser. No. 09/456,410, filed Dec. 8, 1999, titled, “System andMethod for Monitoring Assets, Objects, People and Animals UtilizingImpulse Radio,” and it's parent Ser. No. 09/407,106, filed Sep. 27,1999, both of which are incorporated herein by reference.

Exemplary Transceiver Implementation

Transmitter

An exemplary embodiment of an impulse radio transmitter 602 of animpulse radio communication system having one subcarrier channel willnow be described with reference to FIG. 6.

The transmitter 602 comprises a time base 604 that generates a periodictiming signal 606. The time base 604 typically comprises a voltagecontrolled oscillator (VCO), or the like, having a high timing accuracyand low jitter, on the order of picoseconds (ps). The voltage control toadjust the VCO center frequency is set at calibration to the desiredcenter frequency used to define the transmitter's nominal pulserepetition rate. The periodic timing signal 606 is supplied to aprecision timing generator 608.

The precision timing generator 608 supplies synchronizing signals 610 tothe code source 612 and utilizes the code source output 614 togetherwith an internally generated subcarrier signal (which is optional) andan information signal 616 to generate a modulated, coded timing signal618. The code source 612 comprises a storage device such as a randomaccess memory (RAM), read only memory (ROM), or the like, for storingsuitable PN codes and for outputting the PN codes as a code signal 614.Alternatively, maximum length shift registers or other computationalmeans can be used to generate the PN codes.

An information source 620 supplies the information signal 616 to theprecision timing generator 608. The information signal 616 can be anytype of intelligence, including digital bits representing voice, data,imagery, or the like, analog signals, or complex signals.

A pulse generator 622 uses the modulated, coded timing signal 618 as atrigger to generate output pulses. The output pulses are sent to atransmit antenna 624 via a transmission line 626 coupled thereto. Theoutput pulses are converted into propagating electromagnetic pulses bythe transmit antenna 624. In the present embodiment, the electromagneticpulses are called the emitted signal, and propagate to an impulse radioreceiver 702, such as shown in FIG. 7, through a propagation medium,such as air, in a radio frequency embodiment. In a preferred embodiment,the emitted signal is wide-band or ultrawide-band, approaching amonocycle pulse as in FIG. 1A. However, the emitted signal can bespectrally modified by filtering of the pulses. This bandpass filteringwill cause each monocycle pulse to have more zero crossings (morecycles) in the time domain. In this case, the impulse radio receiver canuse a similar waveform as the template signal in the cross correlatorfor efficient conversion.

Receiver

An exemplary embodiment of an impulse radio receiver (hereinafter calledthe receiver) for the impulse radio communication system is nowdescribed with reference to FIG. 7.

The receiver 702 comprises a receive antenna 704 for receiving apropagated impulse radio signal 706. A received signal 708 is input to across correlator or sampler 710 via a receiver transmission line,coupled to the receive antenna 704, and producing a baseband output 712.

The receiver 702 also includes a precision timing generator 714, whichreceives a periodic timing signal 716 from a receiver time base 718.This time base 718 is adjustable and controllable in time, frequency, orphase, as required by the lock loop in order to lock on the receivedsignal 708. The precision timing generator 714 provides synchronizingsignals 720 to the code source 722 and receives a code control signal724 from the code source 722. The precision timing generator 714utilizes the periodic timing signal 716 and code control signal 724 toproduce a coded timing signal 726. The template generator 728 istriggered by this coded timing signal 726 and produces a train oftemplate signal pulses 730 ideally having waveforms substantiallyequivalent to each pulse of the received signal 708. The code forreceiving a given signal is the same code utilized by the originatingtransmitter to generate the propagated signal. Thus, the timing of thetemplate pulse train matches the timing of the received signal pulsetrain, allowing the received signal 708 to be synchronously sampled inthe correlator 710. The correlator 710 ideally comprises a multiplierfollowed by a short term integrator to sum the multiplier product overthe pulse interval.

The output of the correlator 710 is coupled to a subcarrier demodulator732, which demodulates the subcarrier information signal from thesubcarrier. The purpose of the optional subcarrier process, when used,is to move the information signal away from DC (zero frequency) toimprove immunity to low frequency noise and offsets. The output of thesubcarrier demodulator is then filtered or integrated in the pulsesummation stage 734. A digital system embodiment is shown in FIG. 7. Inthis digital system, a sample and hold 736 samples the output 735 of thepulse summation stage 734 synchronously with the completion of thesummation of a digital bit or symbol. The output of sample and hold 736is then compared with a nominal zero (or reference) signal output in adetector stage 738 to determine an output signal 739 representing thedigital state of the output voltage of sample and hold 736.

The baseband signal 712 is also input to a lowpass filter 742 (alsoreferred to as lock loop filter 742). A control loop comprising thelowpass filter 742, time base 718, precision timing generator 714,template generator 728, and correlator 710 is used to generate an errorsignal 744. The error signal 744 provides adjustments to the adjustabletime base 718 to time position the periodic timing signal 726 inrelation to the position of the received signal 708.

In a transceiver embodiment, substantial economy can be achieved bysharing part or all of several of the functions of the transmitter 602and receiver 702. Some of these include the time base 718, precisiontiming generator 714, code source 722, antenna 704, and the like.

FIGS. 8-9 illustrate the cross correlation process and the correlationfunction. FIG. 8 shows the waveform of a template signal. FIG. 8B showsthe waveform of a received impulse radio signal at a set of severalpossible time offsets. FIG. 9 represents the output of the correlator(multiplier and short time integrator) for each of the time offsets ofFIG. 8B. Thus, this graph does not show a waveform that is a function oftime, but rather a function of time-offset. For any given pulsereceived, there is only one corresponding point which is applicable onthis graph. This is the point corresponding to the time offset of thetemplate signal used to receive that pulse. Further examples and detailsof precision timing can be found described in U.S. Pat. No. 5,677,927,and commonly owned co-pending application Ser. No. 09/146,524, filedSep. 3, 1998, titled “Precision Timing Generator System and Method”,both of which are incorporated herein by reference.

Impulse Radio as Used in the Present Invention

As discussed above, when utilized in an impulse radio virtual wirelesslocal area network of the present invention, the characteristics ofimpulse radio significantly improve the state of the art.

FIG. 10 illustrates the impulse radio virtual wireless local areanetwork 1000 of the present invention. Mobile Unit 1002 can be anydevice desired to input information for transmission via impulse radiotransmitter 1010 associated with mobile unit 1002. The information canbe input into mobile unit 1002 via keyboard 1008, however, it isunderstood that information can be input via voice means such as amicrophone or any other means now known or later developed. In order todisplay information that has been received by impulse radio receiver1006 from impulse radio portal 1016, as well as displaying inputinformation from keyboard 1008, a display 1012 can be associated withmobile unit 1002. Again, although a display is illustrated, any otherdata or voice relation means can be used such as an audio speakerassociated with a mobile phone. The impulse radio portal is a term usedto describe an impulse radio that contains an interface with a networkand provides access to and communication with the network. Thus, theimpulse portal couples the mobile unit to the network. A processor 1004can be incorporated into mobile unit 1002 to control the communicationand data input and display functions. Because most data processing canbe accomplished, via the wireless link between the mobile unit and thelocal area network via the impulse radio portal, at the userscorresponding home computer, the processing power of processor 1004 canbe trivial in relation to the processing power that would be required ifall data processing would be accomplished at the mobile unit itself.

Associated with the individual using the mobile unit is a user tag 1014.The user tag 1014 communicates with the impulse radio portal and themobile unit and provides positioning information of the user and themobile unit and enables the network to know which user it is, therebyenabling connection with that users particular home computer, forexample. Positioning can be accomplished as described above and asdescribed by the impulse radio positioning patents that have beenincorporated herein by reference.

After determining the position of the mobile unit 1002 and associatedtag 1014, the strength of the signal and the signal to noise ratiobetween the mobile unit and the impulse radio portal is measured withinthe impulse radio portal 1016. The signal strength and correspondingposition are then stored in memory 1018. As illustrated above and in theimpulse radio patents incorporated herein by reference, depending on thepropagation characteristics of the environment, impulse radio systemscan modify the data rate and improve the process gain by modifying thepulse integration parameters. Thus, if the mobile unit is in an area ofexcellent propagation characteristics (e.g., close to the impulse radioportal and without barriers to propagation) less processing gain isrequired and, as articulated above and in the corresponding impulseradio patents incorporated herein by reference, the data rate can besignificantly increased.

While the mobile unit 1002 is in motion, the propagation characteristicswill be constantly changing. Further, as the mobile unit 1002 is usedfor various activities, the data rate of the impulse radio transmissionwill vary significantly. For example, if the mobile unit is in voicemode and only voice communications are required within the network, only64 kb/s data rate may be required. However, if the mobile unit isprocessing something complex that requires more computing power, higherdata rates may be required. Also, with the proliferation of the Internetand other data networks, large bandwidth is required to transmitgraphics and similar information.

The impulse radio portal constantly monitors the data throughputrequirements of the mobile unit in relation to the propagationcharacteristics at the position of the mobile unit within the impulseradio portal area. If the propagation characteristics do not support thedata rate required, the impulse radio portal will ascertain from itsmemory 1018 wherein in the impulse radio portal the propagationcharacteristics will support the data rate required and will suggest tothe mobile unit 1002 with corresponding tag 1014 where to move in orderto maintain the data rate requirements.

Impulse radio portal 1016 is interfaced with a gateway 1020 to a localor wide area network. This gateway can be a local computer 1020 or anyother means known to those skilled in the art of accessing a networkedstructure. Once information is received by impulse radio portal 1016,access to the mobile unit user's corresponding computer 1022 ispossible. Once this connection is made, the mobile unit would haveremotely all of the functionality of his home computer as if he werelocated at the computer. Thus if the mobile unit is appropriatelyequipped, the user can answer telephone calls, access email, utilize theword processor or accomplish any computing and communicating taskdesired. Illustrated also in FIG. 10 is the other members of the networkincluding other computers 1024 and 1026.

FIG. 11 at 1100 illustrates zones coveraged by plural impulse radioportals. As shown, mobile unit 1104 is in the zone closest to impulseradio portal 1108. Due to multipath effects caused by metalobstructions, various electromagnetic properties in a given area andother things that may effect propagation characteristics, it may notalways be the case that the nearest impulse radio portal has the bestdata rate possibilities, However, for the sake of a general illustrationit is depicted herein as such. Further, the impulse radio portal takesthe above various propagation factors into consideration whendetermining data rate possibilities by storing in their memorieshistorical positions of the mobile units and the data rates achieved.This information is constantly updated and can be initially stored inmemory during the setup of the impulse radio predefined area by testing.

As shown as relative line thickness 1122, the mobile unit 1104 has thebest data rate with impulse radio portal 1108. Although the mobile unitis also in communication with impulse radio portal 1106 (the second bestdata rate as depicted by moderate thickness line 1120) and impulse radioportal 1110 (the least data rate as depicted by thin line 1118), thedata is entered into the network 1116 via impulse radio portal 1108because the greatest data rate is achieved by this portal. The dataentry impulse radio portal will be referred to as the primary portal.

As the mobile unit moves in relation to the predefined area defined bythe impulse radio portals, it's position and signal strength areconstantly monitored. Once the data has been transmitted to the impulseradio portal, the impulse radio portal interfaces with the network.

The impulse radio portal can, in effect, convert data received from animpulse radio to digital data and will format or packetize the data fortransmission on the network, in accordance with known and future networkprotocols. The impulse radio portal will receive and demodulate intodigital data impulse radio signals received from impulse radios. Thedigital data can be decoded before it is formatted for coupling toanother impulse radio portal or other computing device over the networkvia the network protocol, or it can remain digitally coded and becoupled over the network via network protocol, only to be decoded by thetarget computing device or impulse radio portal. However, sinceanalog-to-digital conversion (ADC), or digital-to-analog conversion(DAC), can occur in the impulse radios (e.g., transmitter, receiver ortransceiver) as they are defined in the patents incorporated byreference, the interface (i.e., impulse radio portal) need not includeADC or DAC capability, but can merely pass digital information and/orpacketize (i.e., format) it for transmission over the network accordingto a compatible network protocol.

The network can be the Internet, or simply an Ethernet, which is themost popular physical layer LAN technology in use today. Ethernet ispopular because it strikes a good balance between speed, cost and easeof installation. These benefits, combined with wide acceptance in thecomputer marketplace and the ability to support virtually all popularnetwork protocols, make Ethernet an ideal networking technology for mostcomputer users today and an ideal interface with the impulse radioportal. The Institute for Electrical and Electronic Engineers (IEEE)defines the Ethernet standard as IEEE Standard 802.3. This standarddefines rules for configuring an Ethernet network as well as specifyinghow elements in an Ethernet network interact with one another. Byadhering to the IEEE standard, network equipment and network protocolscan communicate efficiently and can be easily interfaced with impulseradio portals. Other LAN types include Token Ring, Fast Ethernet, FiberDistributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) andLocalTalk, all of which can also be integrated into the impulse radioportal system by those with ordinary skill in the networking art.

As articulated above and in the referenced impulse radio patents andpatent applications, extremely high data rates are possible. Rates thatmay surpass today's standard Ethernet networks. Thus, for Ethernetnetworks that need higher transmission speeds, the Fast Ethernetstandard (IEEE 802.3u) has been established and can be integrated intothe impulse radio virtual wireless LAN. This standard raises theEthernet speed limit from 10 Megabits per second (Mbps) to 100 Mbps withonly minimal changes to the existing cable structure. There are threetypes of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable,100BASE-FX for use with fiber-optic cable, and 100BASE-T4 which utilizesan extra two wires for use with level 3 UTP cable. The 100BASE-TXstandard has become the most popular due to its close compatibility withthe 10BASE-T Ethernet standard.

Those skilled in the art can modify the system depending on the numberof users in each site on the network that need the higher throughput,decide which segments of the backbone need to be reconfiguredspecifically for 100BASE-T, and then choose the necessary hardware toconnect the 100BASE-T segments with existing 10BASE-T segments. Theseare all networking configurations currently available and which can beinterfaced with the impulse radio portals for the mobility hereindescribed. The aforementioned networking embodiments are described forenabling and illustration purposes only and should not be construed asbeing limited to those networking embodiments. Indeed, it is anticipatedthat as Gigabit Ethernet, which is a future technology that promises amigration path beyond Fast Ethernet so the next generation of networkswill support even higher data transfer speeds, is developed, impulseradio portals will be integrated with those architectures as well.

Token Ring is another form of network configuration which differs fromEthernet in that all messages are transferred in a unidirectional manneralong the ring at all times. Data is transmitted in tokens, which arepassed along the ring and viewed by each device. When a device sees amessage addressed to it, that device copies the message and then marksthat message as being read. As the message makes its way along the ring,it eventually gets back to the sender who now notes that the message wasreceived by the intended device. The sender can then remove the messageand free that token for use by others. Again, it is possible tointegrate impulse radio portals into Token Ring embodiments by thoseskilled in the art.

Once the data has passed via impulse radio techniques to the impulseradio portal and interfaced with one of the networking configurationsabove, the mobile unit 1104 will have wireless access to the network andthereby its home computer 1102. Thus, all functions that can beaccomplished while the user is at its computer 1102 can be accomplishedby using mobile unit 1104. As illustrated, the mobile unit does notnecessarily need to be a “dumb” terminal or a notebook computer, itcould be a wireless communication means 1124 such as a impulse radiocordless communication device, a cellular communication device withimpulse radio integration as described in the patent applicationincorporated herein by reference, an electronic organizer such as a PalmPilot® developed by 3COMM or any other device that can interface with animpulse radio transceiver and communicate information.

FIG. 12 illustrates the flow chart of the method of operation of thevirtual wireless LAN of the present invention. In step 1202 a contact isinitiated between the mobile unit and the impulse radio portals viaimpulse radio communications as described herein and by the impulseradio patents incorporated herein by reference. Once contact isinitiated in step 1202, the impulse radio portal responds andestablishes two-way communication. Because of the unique properties ofimpulse radio, simultaneously the position of the mobile unit can beascertained. Further, as mentioned a TAG can be associated with a user.This TAG can have information concerning who the user is and whichcomputer is his home computer. Other information also can be containedin the TAG as desired for various implementations of the presentembodiment. Positioning using impulse radio is described above and inthe patents and patent applications herein incorporated by reference.Once the positioning information has been obtained in step 1206, in step1208 the correlated information concerning position of the mobile unitand signal strength relative to that position are stored in memory.Determining signal strength is articulated above and in the patents andpatent applications incorporated herein by reference.

In step 1210 a connection is established between the primary impulseradio portal and the local area network. Although herein a local areanetwork is described, it is understood that a wide area network or anynetwork architecture (such as the Internet) is equally applicable forinterface with the impulse radio portal. In step 1214 a determination asto whether or not the mobile unit is moving is made. If YES, thencontinue monitoring the position of the mobile unit and signal strengthin relation to all impulse radio portals. In step, 1222, a determinationis made if the signal strength is strongest with the current impulseradio portal. If NO, then a handoff is made to the impulse radio portalwith the strongest signal (this is now the primary impulse radio portal)and a return to step 1214 is accomplished. If in step 1222, YES isdetermined and therefore the current impulse radio has the strongestsignal, in step 1212 it is determined if the signal strength is adequatefor the data rate sought. As described above and in the patents andpatent applications incorporated herein by reference, signal strengthand data rate are related in impulse radios. Hence, if a low signalstrength and low signal to noise ratio are present, the integration ofmore pulses to retrieve a data bit would be required. Thereby, loweringthe data rate. Thus, if YES in step 212, then the position with thecurrent signal to noise ratio is adequate for the data rate required andno suggested position for the mobile unit is sent.

If, however, in step 1212 it is determined that the signal to noiseratio cannot support the data rate required, the impulse radio portalnotes the present position of the mobile unit, updates the memory withthe location and signal to noise ratio at that position and recalls fromits memory a location near the present location wherein a better signalto noise ratio and therefore higher data rate is present. Any standardpositioning scheme can be employed. For example, the impulse radioportal can have in its memory a data base of available positions or X-Ycoordinates that can be related to the mobile unit. The message isrelated to the user in a meaningful way by simple software algorithms.This will prevent the user from being relocated to a position occupiedby a wall or a desk or other obstruction.

Another positioning scheme which may be used is pre-designated computingareas. This provides more accuracy in signal to noise ratio and datarate information but limits movement flexibility. For example, mobileareas can be marked with designations. The user may be at position 123in room XYZ wherein the data rate is 1 Mbit/sec and be downloading agraphic file wherein 5 Mbit/sec is desired. The impulse radio portal cansuggest a move to position 345 in room XYZ or as an alternate position456 in room ABC wherein because of multipath and distance considerationsprovides a higher data rate. Again, this information is constantlyupdated in the impulse radio signal to noise ration position memory.

While particular embodiments of the invention have been described, itwill be understood, however, that the invention is not limited thereto,since modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. It is, therefore,contemplated by the appended claims to cover any such modifications thatincorporate those features or those improvements which embody the spiritand scope of the present invention, and including existing and futuredeveloped equivalents

1-47. (canceled)
 48. An ultra wideband radio wireless local areanetwork, comprising: a network; at least one ultra wideband radio portalon the network, said ultra wideband radio portal including a first ultrawideband radio transceiver and an interface with the network; and amobile unit, said mobile unit comprising a second ultra wideband radiotransceiver in communication with said first ultra wideband radiotransceiver at a data rate; wherein the data rate varies based on aposition of the mobile unit relative to the ultra wideband radio portaland the position is determined using positioning techniques.